This invention relates to a process for manufacturing polyurethane-coated products wherein a metal material is press-formed into a core member of a desired shape and then the core member is covered with polyurethane foam in place.
The process of this type, i.e. the process, wherein a metal material is press-formed into a core member of a desired shape and thereafter the desired portions of the core member are covered with polyurethane foam, is applied to the manufacture of bumpers and the like as well as internal automotive trim parts such as instrument panel pad, seat, overhead consolebox, door trim, armrest, kneepad and the like.
For example, when the instrument panel pad is manufactured by press-forming a metal material into a core member of a desired shape and then covering the surface of the core member with polyurethane foam, it has hitherto been the practice that a metal material (usually steel plate or galvanized steel plate), which is coated with a rust preventing oil for preventing the generation of rust during the transportation or keeping in the warehouse, is first subjected to a blanking step, coated with a press-forming lubricant (high-viscosity lubricant composed mainly of a mineral oil, for example, trade name "G 634" made by Nippon Kosakuyu Kabushiki Kaisha or the like) and then press-formed into a desired shape. Then, the thus press-formed metal material, has been covered at its necessary surface portions as a core member (which is usually called an insert member) with polyurethane foam. In order to obtain satisfactory adhesion between the core member and the polyurethane coating, however, it was believed to be important that the rust preventing oil previously adhered to the steel surface and the press-forming lubricant applied before the press-forming be completely removed from the surface of the core member and hence the degreasing step is required. The order of production steps for the instrument panel pad is shown in the following Table 1. Such an order of the prior art has drawbacks as mentioned below:
1. The step order becomes complicated. (A number of steps are required and labor is largely consumed.)
2. In order to provide a satisfactory adhered state between the press-formed core material and the polyurethane material after the use of the press-forming lubricant composed mainly of a mineral oil, it is necessary to effect a degreasing and cleaning step for completely removing the rust preventing oil and the press-forming lubricant as mentioned above.
3. Since the press-forming lubricant composed mainly of the mineral oil has frequently a high viscosity so as to sufficiently facilitate the drawing operation, this causes troubles such as partial degreasing or insufficient degreasing and the like. As a result, much labor and time is required to complete the degreasing step.
The degreasing step is commonly considered by those skilled in the art to be essential because it is generally necessary to effect a pretreatment for surface degreasing and cleaning prior to the adhering as shown in ordinary articles, for example, Handbook of Adhesive Technology, Kikkan Kogyo Shinbunsha, July 1963, p 18 et seq. and Polyurethane Resin, Nikkan Kogyo Shinbunsha, 1969, pp 115 and 239. That is, the concept that the degreasing step is an essential step has not been examined to make adhesion complete, widespread in the art and is substantially normalized. As a result, countermeasures for the degreasing step at all.
In general, the surface of the metal material, which is an adherend, is frequently covered with a thin film of an oxide or a hydroxide, or may adsorb various substances. Further, the surface of the adherend is usually contaminated with oils used for rust prevention, oils used for the cutting or rolling, and the like. In this case, these oils are removed with a solvent, a detergent, an acid or an alkali because they adhere to the adherend in a large quantity and considerably reduce the adhesive strength. When using the solvent, however, the partly adhered oil may be spread over the whole surface of the adherend, so that the repeated washing is carried out by successively exchanging the used detergent for new ones. Further, when using the alkali or detergent, these substances remain at the surface of the adherend and hence may reduce the adhesive strength.